First regarding the temperature issues. I resoldered one of the leds from cooper heatsink to aluminium one. When compared with brand new LED on the same heatsink it was clearly visible that old led is heating on much faster rate. Therefore the heat performance on cooper was worse due to the overheating LEDs during soldering.

Also I measured the luminous flux. Maximal value was 869 lumens. The 70 CRI XP-L2 4000K LED topped at 562 lumens, 80 CRI one at 383 lumens. With both leds in 70 CRI variant the lamp should go over 1000 lumens easily.

Anyway, I've finally tested the lamp in small local cave. From mechanical side of view it worked well. The light is quite pleasant and strong enough for my needs. Only drawback is the light stability :) - after hour or so it started blinking and after powering off I wasn't able to turn the main light on again. But that seems to be a firmware issue, I guess disable limit checking magic key combination could be useful.